An AT interface has been used hitherto as one of interfaces for connecting a personal computer and a hard disk drive (HDD). For the AT interface, as shown in FIG. 11, connectors 82 and 83 for two HDDs are connected in a daisy chained configuration to an interface connector 81 for a personal computer, and one HDD serves as a master HDD and the other HDD as a slave HDD. The AT interface defines forty interface lines. Actually, in addition to the forty interface lines, four power lines may be added. FIG. 11 shows forty four lines #1 to #44, which are called interface lines. An HDD has at least a hard disk for storing information, a read/write head, a spindle motor for rotating the hard disk, and a circuit board. Provided on the circuit board are at least a read/write circuit, a head driving circuit, a motor driving circuit, an interface circuit, a control circuit for controlling these circuits, and the connector 82 (or 83) connected to the interface lines.
To use one HDD as a master HDD or a first HDD and the other HDD as a slave HDD, or a second HDD, control signals indicating a master and a slave must be supplied to controllers for two HDDs. When a controller detects the control signal indicating a master, that HDD operates as a master HDD. On the other hand, when a controller detects the control signal indicating a slave, then that HDD operates as a slave HDD.
There are two methods of supplying a control signal indicating a master or a slave to a controller for an HDD. A first method is to equip the HDD with switch means to supply a signal indicating a master (for example, a low-voltage level signal) or a signal indicating a slave (for example, a high-voltage level signal) to the control circuit on the HDD. Such selection by the switch means, which is independent of the interface lines, is called local selection. Pins #45, #46, #47, and #48 shown in FIG. 11 serve as the switch means for local selection. The pins #45 to #48 are not connected to the interface lines.
In the following, the construction of the connectors 82 and 83 is described in further detail. A construction of the connector 83 is the same as that of the connector 82. FIG. 12 shows the construction of the connector and a jumper plug. Showed in FIG. 15 is the electrical connection of the pins #45 to #48.
The pins #45 and #46 are electrically floating, that is, are not tied to any voltage, and accordingly a voltage at the pin #45 and #46 is referred to as a floating voltage. The pin #47 is tied to a reference potential, for example, a ground potential, and the pin #48 is tied to a potential (for example, +5 V) different from the reference potential through a line 90 and a resistance 91. The controller for an HDD determines whether the HDD was specified as a master HDD or a slave HDD by detecting a potential at a terminal 92. The specification of master HDD is implemented through the selective connection of two pins #47 and #48 by an operator or a user, and the specification of slave HDD is implemented by keeping two pins #47 and #48 from their connection.
Referring to FIG. 13 and FIG. 14, a jumper block 93 is used to connect the pin #47 and the pin #48. The jumper block 93 is made of an insulating material and includes conductive accept members, that is, a first and second jumper connections 94 and 95, which accept the pins, and a conductor 96 for electrically connecting the accept members 94 and 95 to each other. As shown in FIG. 13, the pins #47 and #48 are connected when the jumper plug 93 is inserted into the pins #47 and #48 by the operator, thus the terminal 92 is tied to the reference potential (a low voltage level). The controller for the HDD detects the low voltage level, and thereby the HDD serves as a master HDD.
As shown in FIG. 14, when the jumper block 93 is inserted into the pins #45 and #46, a potential at the terminal 92 is +5 V and then the controller for the HDD detects a high voltage level, and thereby the HDD serves as a slave HDD.
A second method follows cable selection determined based on the AT Attachment Specification of American National Standard for Information Systems. In the second method, a potential at the interface line #28 shown in FIG. 11 specifies a master or slave. The interface line 28 of the connector 81 for the personal computer is tied to the reference potential (0 V), as shown in FIG. 11.
The connector 83 is kept from being tied to the reference potential by the user, as indicated by a dotted line 80. That is, a voltage at a pin #28 of the connector 83 is open, that is, floating. This open voltage represents a slave, and accordingly the controller for the HDD connected to the connector 83 recognizes itself as a slave by detecting the voltage at the pin #28.
The pin #28 of the connector 82 is tied to the reference potential, and accordingly the HDD connected to the connector 82 recognizes itself as a master by detecting the voltage at the pin #28.
To support both local selection and cable selection, two switch means are conventionally required. First switch means is necessary for selecting either local or cable selection, and second switch means is used for selecting either a high voltage level representing a slave or a low voltage level representing a master when local selection is selected by the first switch means. Such a conventional method involves the following problems. That is, a user must operate the first and second switch means, and a controller first determines to see whether an operation mode is local selection or cable selection by checking the output voltage of the first switch means, and must check a voltage at the interface line #28 if the first switch means was changed to the cable selection mode or check the voltage level of the second switch means if the first switch means was changed to the local selection mode to recognize a master or slave.